The view that we should avoid eating meat or fish has ancient philosophical
roots. In the Hindu
Upanishads
(about 1000 BC) the doctrine of
reincarnation leads to opposition to eating meat. Buddha taught compassion for
all sentient creatures. Buddhist monks were not to kill animals, nor
to eat meat, unless they knew that the animal had not been killed for their
sake. Jains hold to ahimsa, or non-violence toward
any living creature, and accordingly do not eat meat.

In the Western tradition, Genesis suggests that the first diet of human
beings was vegetarian, and permission to eat meat was given only after the
Flood. After that, vegetarianism gains little support from either the Jewish or
Christian scriptures, or from Islam. Philosophical vegetarianism was stronger in
ancient Greece and Rome: it was supported by Pythagoras, Empedocles, Plutarch,
Plotinus, Porphyry, and, in some passages, Plato. Pythagoreans abstained from
eating animals partly because of their belief that humans and animals share a
common soul, and partly because they appear to have considered the diet a
healthier one. Plato shared both these views to some extent. Plutarch's essay On Eating Flesh, written in the late first or early second century of the
Christian era, is a detailed argument for vegetarianism on grounds of justice
and humane treatment of animals.

Interest in vegetarianism revived in the nineteenth century, on grounds of
health and humanity towards animals. Notable vegetarian thinkers included the
poet Percy Bysshe Shelley, Henry Salt (who wrote a pioneering volume entitled Animals' Rights), and George Bernard Shaw, who said that he put into his
plays the ideas that he learned from Salt. In Germany Arthur Schopenhauer urged
that ethically we should become vegetarian, were it not for the fact that the
human race cannot exist without animal food 'in the north'!

Since the 1970s vegetarianism has gained strength from three major lines of
argument: health, ecology, and concern for animals. The first of these grounds
rests on a scientific, rather than philosophical, claim and will not be
discussed further here. Ecological concerns about eating meat arise from the
well-documented inefficiency of much animal-raising. This applies especially to
intensive farming, in which grain is grown on good agricultural land and fed to
animals confined indoors, or in the case of cattle, in crowded feed-lots. Much
of the nutritional value of the grain is lost in the process, and this form of
animal production is also energy-intensive. Hence concern for world hunger, for
the land, and for energy conservation provide an ethical basis for a vegetarian
diet, or at least one in which meat consumption is minimized.

Arguments for a reassessment of the moral status of animals have also given
support to vegetarianism. If animals have rights, or are entitled to have their
interests given equal consideration with the similar interests of human beings,
it is easy to see that there are difficulties in claiming that we are entitled
to eat non-human animals (but not, presumably, human beings, even if through
some accident they are at a similar mental level to the animals we do eat).
These ethical arguments for vegetarianism may be based on the view that we
violate the rights of animals when we kill them for our food, or on the more
utilitarian grounds that, in raising them for our food, we cause them more
suffering than we gain by eating their flesh.